IP Multimedia Subsystem (IMS) based services have been successfully deployed in 4G mobile networks. Voice over LTE (VoLTE) services are taking over the role of circuit switched 2G and 3G technologies. VoLTE enables higher quality services and more efficient transmission and radio spectrum utilization than previous 2G and 3G technologies.
Taking advantage of IMS, 4G mobile networks also enable other advanced services, like video telephony over LTE (ViLTE) and Rich Communications Services (RCS). Example of RCS are instant messages, audio and video messaging, file sharing or other services.
Circuit-switched technologies in 2G and 3G networks for voice services provide well defined and guaranteed quality of services for voice. The expectation of users is that newer technologies provide even better service quality. The success of new services also depends significantly on the user experience.
Network operators use customer experience management (CEM) systems to monitor quality of experience (QoE) of the subscribers. CEM system collects event and counter information from several parts of the network and calculate KPIs (Key Performance Indicators) from correlated data. These are classified by 3GPP as accessibility, retainability, mobility and integrity KPIs. One of the most important integrity KPIs is the mean opinion score (MOS) of multimedia services.
ITU-T standardized a methodology estimating audio, video and audio-video MOS (ITU-T 1201.1). It is very complex solution containing around 10-12 parameters, lot of side information that cannot be obtained directly from the network data sources. Originally, MOS reflects the perceived voice, video, or audio-video quality, in scale of 1-5, measured in laboratory human tests. MOS depends on many factors, starting from the codec type, rate of the multimedia flow, the signal processing of the multimedia devices, the bandwidth and any other impairment of the media that may occur during transmission: packet loss, delay, and jitter. There have been several attempts to estimate the MOS for different multimedia types and estimating the different impairment factors affecting MOS. ITU-T has standardized P800.1 the measuring method of assessing objective and subjective quality of voice in a telephone network. ITU-T 1201.1 and 2 specify an algorithm and model for monitoring and estimating audio, video and audio-video MOS.
This kind of information can be obtained only by installing software on the entity to which the data stream is transmitted, e.g. the mobile phone. The large number of parameters makes the formula uncertain and in a mobile communications network is not really possible to install the same software on each mobile phone.
This means that the implementation of the model it is not really feasible. Besides that, the model does not handle the quality degradation provoked by the propagation of frame errors and it takes into account only the loss of frame, but not the degree of frame loss.
Accordingly, the need exists to provide a method which facilitates the estimation of losses in a video stream.